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I'm building a loft bed for a queen size bed. I planned to build a platform and support it with 4x4s, but I'm having trouble finding untreated 4x4s. I plan to loft the bed 5' or so. The platform will be made of 2x6's covered in 1/2" plywood.

This shows what I'm planning to do:

enter image description here

Can I use two 2x4s instead of the 4x4's to carry the load?

If so, will nailing/screwing them together in several places be sufficient to hold them together?

I'd like to use 3/8" bolts to join the platform to the posts (for easy disassembly). If so, should I only bolt down the long side of the platform, or try to place bolts on both sides of the corner? If the latter, how should I put a bolt through the narrow side of the joined boards?

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3 Answers 3

2 2x4s are not square, if that matters (3 x 3.5). They will be plenty strong as assembled posts.

Try a traditional lumber yard, they will have untreated pine. Cedar may also be an option.

Your structure would be better supported if you shortened 1 of the 2 paired 2x4s at each corner and made a jack-king stud arrangement like a door frame and header. The main tenant of construction is to bear the weight with structural components and only use fasteners to keep the structure in place, not to bear the load (in shear).

You are, in effect, making a small deck. You should attach the rear 2x8 2x6 to each wall stud. A 4" #10 decking screw would not be too small .

The front and rear members are, in effect, beams and should be 2x8s. The joists running perpendicular to the beam should be 2x6 2x4s hung with joist brackets.

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Yes it is a deck of sorts, but instead of a 60psf live load for a crowd of people dancing, for which your size recommendations are completely appropriate, we're looking at more like 15psf live load for 2 people, um... "dancing". 2x4 joists and 2x6 beam will be fine, IMO. Compare with the member sizes often seen in commercial bed frames. I feel like I'm nit-picking you with minor details, even though you always have excellent answers. I call 'em as I see 'em. – bcworkz Apr 6 '13 at 21:03
I'd go for a bit of downsizing, if they did the jack/king, lagged one side and used hangers. Anyone mamboing up in the air may draw a crowd... – HerrBag Apr 6 '13 at 21:10
Thanks for the help! Could you give some advice about how I should attach the posts to the platform? I'd like to use removable fasteners (e.g. bolts) so I can move the thing from time to time. I'm not sure how many and where is good to place them. I'm also not positive how I should attach the "jack" stud to the platform (without nails). The images below are what I think should work, but I'd love some input. Outside Inside – bradreaves Apr 8 '13 at 2:32
Your jack is correct, forming a ledge for the beam (front and rear 2x6s) No beam to jack connector (toe nails or such) are needed. The king to jack connections (a pair of screws every 12") will solidify the beam. I would spread your upper and lower face bolts (beam to king) on either side of the king center line.. 1" either side of centerline. If you use carriage bolts, be sure to use washers on the inside.. Pine is quite soft and they will bury. I would use deck screws in place of nails.. 3" for framing connections. Screw down your plywood into all beams and joist. – HerrBag Apr 8 '13 at 3:39
I would use construction adhesive at all plywood to structure contact. (I favor polyurethane adhesive) – HerrBag Apr 8 '13 at 3:41

If you are going to use 2x4 instead of 4x4's as "beams" I'd set them on edge. If you glue and nail them that will be stronger than just nailing them together. I'd also consider using a metal bed frame with the legs removed on top, rather than plywood (as long as you're using a box spring). The plywood is going to sag a lot across that span, enough that the side walls are going to tilt in in front. Also, this thing is going to want to rack over without corner bracing.

But really I think you're reinventing the wheel quite a bit. You could modify standard framing methods just a little and get something sturdy. Google around "platform framing" "balloon framing" "post and beam" and get some ideas from centuries of carpentry.

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You need to put the 2x4s on edge, not flat. Consider a large, soft covered book. We used to call them phone books, but no one knows what they are any more. Hold the book with the spine in one hand, and the open end in the other. Give the book a bend. You'll see the pages separate in the middle.

The same thing happens in a beam. So if you lay the 2x4s flat, you'll get the same effect. (If you have to lay them flat, you must clamp and glue them.)

I also have some concerns with the way you are mounting the beams to the walls. You're asking your connector to support the entire load. I'd much rather see the studs rotated 90 degrees, as in traditional wall framing and have the beams run on top. Use a connector, such as this:

enter image description here

You might be able to find something a bit more decorative at a specialty hardware store.

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I believe those 2x4's are vertical and the picture is as seen from the floor (or actually under the floor). – BMitch Oct 8 at 20:56
Oh Wow! It looks like I had the wrong perspective on this. Will rewrite answer, later. But the beams should still be on top of the posts. – Chris Cudmore Oct 9 at 18:31

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